[Haskell-cafe] commutative monoid?

[Brent Yorgey]

On Sat, Jun 25, 2011 at 02:34:47PM -0700, Evan Laforge wrote:
> On Sat, Jun 25, 2011 at 2:02 PM, Brent Yorgey <byorgey at seas.upenn.edu> wrote:
> > Actually, there are (at least) four: there's also the one where
> > mappend = liftA2 mappend, i.e. introduce potential failure into a
> > monoid operation defined on the values.  I wrote about it here:
> >
> >    http://byorgey.wordpress.com/2011/04/18/monoids-for-maybe/
> 
> Just out of curiosity, what was the problem that wanted this kind of
> monoid for the solution?  I always find concrete examples useful in
> addition to the abstract explorations and toy examples.

To be honest, I don't remember!

-Brent